There are several medical indications for which vascular occlusion is an appropriate treatment including, for example, for rerouting blood to a different part of a patient's body, for reducing or halting supply of blood to a tumour or other growth, for reducing the supply of blood to an organ or area of a patient's body prior to a medical procedure or treatment, for reducing pressure on a fistular, weakened or leaking blood vessel, and so on.
Conventionally, vascular occlusion was effected by surgically closing or ligating the blood vessel, which required an open surgical procedure with inherent risks and complications. More recently, vascular occlusion has been effected by the endoluminal implantation into a patient of one or more implantable medical devices. A well-known device is in the form of a wire coil which can be implanted in a patient's vasculature and which effects occlusion by promoting embolization of blood, usually by means of fibres attached along the length of the wire coil. Typically, several such coils are implanted, one adjacent the other in the vessel, until the clinician is satisfied that adequate occlusion has been achieved. Such a procedure can take time to reach adequate occlusion. Moreover, the length of the occluding barrier produced by the implanted coils will vary in dependence upon the number of coils implanted and the size of the vessel. This is not, though, always practicable.
It is also known to effect occlusion by administration of a thrombogenic agent into a patient, for instance by injection of such agent between two spaced balloons which are inflated in a patient's vessel. The thrombogenic agent assists in the creation of a blood clot between the inflated balloons, which can then be removed so as not to leave in the patient's body any foreign device. The balloons can also provide an occluding barrier of predetermined length, suitable for locations where there is limited vascular space.
As well as issues of length of the occluding barrier which may be necessary, and thus of accommodation in a patient's vasculature, occlusion can also be prone to recanalization, that is to leakage through the occluding barrier and eventual reopening of the vessel. Such shortcomings can occur with the devices and methods described above.
Vascular occluders can also suffer from migration within the vessel, caused by the pressure of blood on the occluder, as well as by changes in the size and shape of the vessel over time and during normal bodily functioning. Migration can result in loss of the occlusion seal, and thus of blood leakage past the occluder, blockage of unwanted vessels including side branches, and so on.